1. Field of the Invention
The invention concerns a gas generator for deploying and inflating at least one impact cushion of a passenger restraint system, with a gas generator housing, which has at least one seal, for holding a propellant for generating a quantity of inflating gas for each impact cushion. The invention also concerns a passenger restraint system for vehicles and a method of inflating and deploying at least one impact cushion of a passenger restraint system of this type.
2. Description of the Related Art
Passenger restraint systems are used in vehicles of all types, especially land vehicles, boats, and aircraft.
State-of-the-art restraint systems of this type, which are also known as air bags or airbag systems, consist of a device for generating the required quantity of inflating gas (gas generator), an impact cushion, which usually consists of a textile material, and an activating and monitoring unit that controls and/or regulates the gas generator. In the event of a vehicle collision, the impact cushion prevents passengers from striking interior parts of the vehicle, such as the steering wheel or the side panels. In motor vehicles, the activating and monitoring unit is usually housed in the central tunnel near the gear-shifting gate.
Pyrotechnic gas generators are distinguished from so-called hybrid gas generators. In pyrotechnic gas generators, the gas is generated by a pyrotechnic propellant, which is ignited in an emergency. The nitrogen gas formed by the consumption of the propellant enters the impact cushion through holes in the gas generator housing and deploys and inflates the impact cushion in about 30 ms. The propellant charge is ignited by an ignition unit (AZE) which is ignited by an electrical pulse generated by the activating and monitoring unit. The pyrotechnic propellant is composed of sodium azide/calcium nitrate/sand and is pressed into tablet form. Since this propellant is a toxic substance, it is being replaced more and more by propellants that do not contain sodium azide. However, these propellants have the disadvantage that they produce combustion gases with very high gas temperatures and a very high cinder content.
A variation on the pyrotechnic gas generator is the hybrid gas generator design. The volume of inflating gas is generated mostly by an inflating gas supplied from a compressed-gas cylinder under high pressure (e.g., argon at about 300 bars) and to a small extent by combustion of a pyrotechnic propellant. The pyrotechnic propellant opens the compressed-gas cylinder, which contains a gas mixture pressurized to as much as 250 bars, and heats the escaping inflating gas to prevent the seals and gas delivery channels from freezing up due to the cooling produced by the expansion. Hybrid gas generators are used in motor vehicles for driver air bags, passenger air bags, and side air bags.
The use of pyrotechnic propellants in both pyrotechnic gas generators and hybrid gas generators imposes exacting requirements on the manufacture and installation of the system components:
The combustion of pyrotechnic propellant charges produces temperatures of up to 2,000° C. The potential danger associated with these high temperatures is tolerated with a good deal of justification (considering the life-saving action of the restraint system).
Another problem associated with pyrotechnic restraint systems is their disposal. This requires careful and completely safe dismantling and neutralization of the propellant charges. Uncontrolled disposal of used vehicles with pyrotechnic propellants or propellant charge components is a significant safety and environmental hazard.
In order to reduce the high temperatures and high cinder content of the combustion gases in pyrotechnic gas generators with azide-free propellants, DE 196 125 81 A1 has already proposed a gas generator in which the combustion chamber contains, in addition to the pyrotechnic propellant, a vaporizable substance placed in front of the discharge ports. Energy exchange between the combustion gas and the vaporizable substance makes it possible to maintain the energy content of the pyrotechnic propellant with only slight losses, so there is adequate energy to deploy and inflate the impact cushion. The energy exchange causes vaporization of the vaporizable substance, which in turn causes cooling of the combustion gas and thus a reduction of the cinder substances. The inflating gas for the impact cushion consists primarily of the combustion gas of the pyrotechnic propellant and the vapor produced as a result of the energy exchange. An advantage of this measure that is specified in the cited document is that the thermal energy of the combustion gas is used to vaporize the vaporizable substance, and the combustion gas is not cooled by parts of the housing.
Although the use of a vaporizable substance as a supplementary measure in the gas generator lowers the temperature of the inflating gas and allows the use of nontoxic pyrotechnic propellants, it does not satisfactorily address other requirements on gas generators. Requirements of particular concern are safe handling of the gas generator, thermal stability, environmentally safe disposal, and inexpensive manufacture.
Therefore, proceeding from this state of the art, the goal of the invention is the development of a gas generator for a passenger restraint system which better satisfies the specified requirements while still using nontoxic starting materials. An additional goal of the invention is the development of a method for generating a volume of inflating gas for an impact cushion of a passenger restraint system.